1. Field of the Invention
This invention relates to a novel apparatus and system for proportioning and mixing a solvent which is made up of a plurality of liquid components. More particularly, it relates to such an apparatus and system in which the liquid components of the solvent are both proportioned and mixed in a single chamber.
2. Description of the Prior Art
It is conventional practice in liquid chromatography to introduce samples to be analyzed to a chromatographic column in a carrier solvent. The carrier solvent typically consists of a mixture of two or more liquid components. During the analysis, the proportions of the liquid components in the solvent may be varied on a linear or non-linear time varying basis. A variety of techniques are known in the art for providing such varying solvent mixtures to the chromatographic columns. For example, U.S. Pat. No. 4,063,077 discloses programmable control circuitry for a valve to access liquid components of a solvent mixture during a defined cycle of operation to proportion the components of the solvent on the basis of the time within the cycle of operation that each component is accessed by the valve. The accessed components are supplied through the valve and a pump to a separate mixer to produce the solvent mixture. U.S. Pat. No. 4,239,623 discloses a system in which each liquid component of the solvent is accessed by separate valves, operated by separate stepper motors. U.S. Pat. No. 4,310,420 discloses a system in which the liquid components of the solvent are separately accessed by solenoid valves. While these prior art systems have proved to be highly suitable for supplying chromatographic solvents, they are both complex and bulky because the liquid component proportioning and mixing are accomplished separately. Because of their size, they also have a delayed response time for the variations in solvent composition. For reasons of compactness and cost, there is a need for a simpler apparatus and system for proportioning and mixing liquid components of a solvent.